My favorite response to diversity hawks is:
"So, you say we need more minorities to have more diversity? Can you tell me how minorities are inherently different from whites? Do they eat different foods, listen to different music, are they better athletes? What is different about them?"
I don't think we need more of anything to be diverse. We just need to be able to accept that everyone has a unique history and origin and that's okay. That's my own personal definition, apparently.